I was out and about last night and was driving around with the heater on max since temperatures took a big nose dive Sunday night. I had a short section at highway speeds (100 km/hr) and noticed that my engine temperature gauge had dropped to just a little bit over 70 C after about 6 km (its an aftermarket gauge with numbers!). Outside temperatures were probably around - 6C so not incredibly cold. When I reduced speed to urban driving the temperature started to climb back up; but, it never reached its typical operating temperature which is usually around 85-87 C (its the 82C opening thermostat).

I am thinking that the thermostat gasket is leaking or the thermostat is no longer closing. Whether its the gasket or the thermostat, its getting a new version of both. I have to lower the fluid level to check so I am having the parts on hand ahead of time so I don't have to do it twice. I remember reading a lot of opinions on good versus junk thermostats for the B20. What is the received wisdom as to what is acceptable; Stant, Gates, Wahler, Beck Arnley .....?